As an ultra-low floor bus does not have doorway stairs compared to an existing city bus and a bottom is flat, an ultra-low floor bus is a vehicle that is developed specially for convenient use by vulnerable people such as elderly people and pregnant women.
However, as a height of a floor bottom is lowered in the ultra-low floor bus, a CNG (compressed natural gas) tank is mounted on a roof, and the ultra-low floor bus becomes heavy by about two tons compared with the general city bus to reinforce a raised mass center and a roof structure such that a fuel consumption as 1.7 KM/M3 is reduced by about 23% compared with the fuel consumption of the general city bus as 2.2 KM/M3.
On the other hand, a vehicle price is more expensive than the general city bus in the ultra-low floor bus, and customer complaints are high due to a low fuel consumption efficiency for the vehicle price. Accordingly, a weight reduction is indispensable to improve the fuel consumption of the ultra-low floor bus.
Patent documents Korean Patent Publication No. 10/2001/0066512 and Korean Patent Publication No. 10/2004/0085292 disclose subject matter that is related to subject matter disclosed herein.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.